The color of light reflected off of a subject changes with the color of the light source. Unlike a human eye, a digital camera is unable to adapt to these changes. The human eye/brain automatically compensates for the color temperature of light falling on an object. When you move from the bright, blue-tinted sunlight to the dim, yellow-tinted indoor lighting, your eye automatically adjusts to the different color of light and changes your perception accordingly. If your brain knows it is looking at something white, it will look white in bright sunlight or inside even under a fluorescent light. Unfortunately, even the most expensive video cameras cannot automatically do what the eye does, so we have to show our cameras what we want them to read as “white” in any given scene.
In most digital cameras, the illumination intensity and color temperature must be measured and adjusted to ensure that a white object is recorded as white. This process is often referred to as white balancing, and is a software or hardware option on all digital cameras. It is important with digital cameras to white balance manually for the absolute best video output results.
White balancing is an important function that is carried out with all digital endoscopic and laparoscopic cameras prior to videoscopic medical procedures. Normally our eyes compensate for lighting conditions with different color temperatures. A digital camera needs to find a reference point which represents white. It will then calculate all the other colors based on this white point.
The RGB system is one of the primary color models used to specify and represent colors in computer-controlled cameras and software. White is produced by combining equal parts of all three colors (red, green and blue) at levels of 100 percent. In white balancing a camera, a sensor on or within the camera averages the light within the scene and automatically adjusts the camera's internal color balance to zero-out any generalized color bias. By finding the difference between the white the camera sees and that of the internal reference white, the camera can adjust for the difference for every other color, thereby generating a more accurate and realistic video image. Even professional photographers who use digital still cameras carry a white reference card to properly white balance in order to capture the most accurate life-like images. It is amazing that today, in the advanced medical procedures requiring realistic and accurate video images, white balancing is rarely done correctly.
The video color quality is very much dependant on the accuracy of the white balance performed prior to the medical procedure. This is especially important in laparoscopic and endoscopic cameras that are involved in life and death situations. A realistic video image is crucial when trying to differentiate between slight pigmentation changes in tissues while looking for inflammation, metastasis during cancer resections or diagnostic procedures.
Often, doctors do not understand the importance of white balancing and so they will use a reference such as surgical gauze—which is actually full of holes and not truly white—to set the calibration. Moreover, white balancing is carried out in the open room where there is different light sources illuminating the “white” gauze sponge; this is a problem because the video inside the body will be generated using only the camera's fiber optic light source. Both of these mistakes generate an incorrect white balance point. Consequently, the video images generated often have a color shift away from the real colors. For photography, this is annoying. For medicine this can be dangerous. Moreover, doctors also often hold the scope too close to the white target distorting the camera's light, or too far exposing the white to room fluorescent lights and spot lights.
Laparoscopic and endoscopic cameras are involved in life and death situations, such as trying to differentiate between slight pigmentation changes in tissues when looking for inflammation or metastasis during cancer resections. Another problem is that, currently, white balancing the medical videoscope during medical procedures is a hassle. The surgeon has to coordinate with the nurse for the right time to white balance. The doctor is often sterile and cannot press the white balance button on the camera equipment. He or she must hold the sterile scope facing the “white” gauze and at the same time synchronize with the nurse to press the white balance button in the equipment. This becomes complicated and time consuming because the nurse often is busy when the surgeon is ready to white balance or the surgeon is busy when the nurse is ready to white balance. This wastes time, and time is very expensive in the operating room.
Additionally, from the birth of endoscopic and laparoscopic surgery to the present, surgeons have continually dealt with a persistent and annoying problem, the fogging of the scope lens. The fogging of the scope is very costly. When scopes fog up during surgery, the surgeon cannot see and must pause the surgery until the picture can be cleared up. This routine commonly occurs at least several times during every procedure. With the incredible costs relating to anesthesia and surgical staff, the wasted time in the aggregate equals hundreds and thousands of dollars.
Condensation on the lens occurs because there are temperature differences which occur initially when the cold scope enters the warm moist body, and transiently during the procedure when the doctor coagulates tissue. Since many medical procedures are sterile, current methods to solve both these visualization problems are limited to messy anti-fog solutions and inaccurate white balancing techniques.
Another major problem is that the white reference must often be sterile, so doctors typically use the “white” surgical gauze sponge to white balance. These sponges are in reality full of holes and actually not the ideal white. By white balancing with an off-white, that is illuminated by different lights with different color temperatures, doctors are settling for below optimum video image quality. Ultimately, this may distort the accuracy of the white balance and diminish the quality and the true reproduction of the color in the video generated from inside the body during the medical procedure. Having below optimum video color quality could be dangerous as inflammation and cancer metastasis often presents as discreet color changes. This is becoming more and more important as endoscopes and laparoscopes are becoming vital diagnostic instruments.